The invention relates to a method and devices for producing granulates from pulverulent, granular, doughy or similar material, more particularly plastics, in which the material to be granulated is formed into a skin between two rotating curved surfaces, for instance, of rollers, the skin form of material being divided into granulates.
Very different types of methods and devices for the manufacture of granulates are known. For instance, German Pat. Specification No. 972,903 discloses an apparatus for granulating pulverulent, pasty or doughy materials, the apparatus including a cylindrical or conical tube formed with sieve-like perforations and utilizing a conveyor or press screw. One or more rotary blades are guided along the sieve surface to divide up the extruded mouldings. The material to be granulated is conveyed by means of a conveyor screw into the granulating apparatus. If suitably constructed, the conveyor screw can precompact the material. By means of a pressure roller formed with corresponding conveying grooves, the material is forced directly, without any definable kneading, through the moulding apertures and then divided into granulates by means of the rotating blades. There is neither the possibility nor the intention of compacting or compressing the material before granulation, for instance, to eliminate any gases which may be enclosed or to make sure that the material is satisfactorily homogenized.
Granulating apparatuses are also known, for instance, from German Auslegeschrift No. 1 242 846, in which the material to be granulated is granulated not immediately after being fed into the apparatus, but only after a suitable compacting phase. However, the phase is much too short, since the material is compacted only at the point of contact of the moulding rollers. The material to be granulated is compacted to some extent, in dependence on its texture, but not adequately homogenized during compacting.